| Autor: |
Harrison, J K, Hewlett, G H, Gnegy, M E |
| Zdroj: |
Journal of Biological Chemistry; September 1989, Vol. 264 Issue: 27 p15880-15885, 6p |
| Abstrakt: |
Studies in bovine and rat brain membranes have suggested that calmodulin can potentiate neurotransmitter- and GTP-stimulated adenylate cyclase activities. To examine whether calmodulin and the stimulatory G-protein, Gs, are potentiative at a calmodulin-sensitive adenylate cyclase, Gs, was purified from rabbit liver and reconstituted with a partially purified calmodulin-sensitive adenylate cyclase from bovine brain. Activated Gs(Gs*) stimulated basal adenylate cyclase activity and enhanced the stimulation by calmodulin. The potentiation of the calmodulin-stimulated adenylate cyclase activity was dose-dependent with respect to Gs* concentration. At the highest concentration of Gs* tested (3 nM), a 2-fold enhancement of the calmodulin-stimulated adenylate cyclase activity was observed at all concentrations of calmodulin. The synergistic activation of adenylate cyclase by calmodulin and Gswas dependent on the presence of Ca2+and occurred at physiologically relevant Ca2+concentrations. The potentiation was not observed when either a nonactivated Gsor a mixture of activated Gi/Gowas used. Gs* was not able to stimulate or potentiate a calmodulin-stimulated adenylate cyclase purified from membranes pretreated with the nonhydrolyzable GTP analog, guanyl-5′-yl β,γ-imidodiphosphate. Photochemical cross-linking of 125I-calmodulin-diazopyruvamide to proteins having an Mrcorresponding to the known Mrof adenylate cyclase was not enhanced by Gs*. The results demonstrate that the guanyl nucleotide-dependent enhancement of calmodulin-stimulated adenylate cyclase activity is mediated by Gs* and suggest that Gs* modulates the enzymatic turnover of the calmodulin-stimulated activity. |
| Databáze: |
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